Mother's occupation and sex ratio at birth

We investigated the effects of mother's age, maternal and paternal job type (and associated psychological stress levels) and paternal income on sex ratio at birth. Our analyses were based on 16,384 incidences of birth from a six-year (2000 to 2005 inclusive) childbirth dataset from Addenbrooke's Hospital in Cambridge, UK. We obtained a restricted data set from Addenbrooke's hospital with: maternal age, maternal and paternal occupations, and whether or not the child was first-born.Women in job types that were categorized as "high stress" were more likely to give birth to daughters, whereas women in job types that were categorized as "low stress" had equal sex ratios or a slight male bias in offspring. We also investigated whether maternal age, and her partner's income could be associated with reversed offspring sex ratio. We found no association between mother's age, her partner's job stress category or partner income on child sex. However, there was an important interaction between job stress category and partner income in some of the analyses. Partner income appears to attenuate the association between maternal job stress and sex ratios at moderate-income levels, and reverse it at high-income levels.To our knowledge this is the first report on the association between women's job type stress categories and offspring sex ratio in humans, and the potential mitigating effect of their partners' income.Psychological stress is omnipresent in our everyday lives. Studies have established links between 1) job stress and coronary heart disease [1,2] slower recovery from injuries [3], depression, and anxiety [4], 2) between maternal psychological stress and suppressed cell-mediated immunity [4], 3) between cortisol levels and preterm deliveries [5,6], or 4) between maternal psychological stress and early foetal abortions[6]. Offspring sex-ratio biases have been observed in human populations under a variety of stress-inducing circumstances such as economic collapse [7], earthqu